1. Field of the Invention
The present invention relates to an image forming apparatus, and a process cartridge detachably attachable to the apparatus main body of an image forming apparatus.
An image forming apparatus is an apparatus configured to form an image on a recording medium by employing the electrophotographic image forming process. Examples of the image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (e.g., a laser beam printer or a light-emitting diode (LED) printer), a facsimile apparatus, and a word processor.
A process cartridge is configured to integrate into a cartridge an image bearing member on which a developer image is formed and at least a developer carrying member as a process unit acting on this image bearing member. The process cartridge is detachably attachable to the main body of an image forming apparatus.
The term “image forming apparatus main body (hereinafter referred to as the apparatus main body) refers to the portion of an image forming apparatus excluding the process cartridge.
2. Description of the Related Art
Conventionally, in the image forming apparatus, a process cartridge system is employed which is configured to integrate into a cartridge a photosensitive drum and a process unit acting on the photosensitive drum. The cartridge is detachably attachable to the apparatus main body.
According to this process cartridge system, the image forming apparatus can be maintained by the user himself without depending on a serviceman, which has achieved a substantial improvement in terms of operability. Thus, this process cartridge system is widely employed in image forming apparatuses.
The process cartridge is divided into a photosensitive drum unit having a photosensitive drum, and a developing unit having a developing roller. Further, the developing unit is capable of movement relative to the photosensitive drum unit.
As an electrophotographic developing system, there is available a contact developing system in which an image is formed with an elastic layer of the developing roller being held in contact with the surface of the photosensitive drum. In this contact developing system, at the time of image formation, the developing roller is in contact with the surface of the photosensitive drum at a predetermined pressure. In this system, when the elastic layer of the developing roller and the photosensitive drum are held in contact for a long period of time from the factory shipment of the process cartridge until its deliverance to the user, there is a fear that the elastic layer of the developing roller may undergo deformation.
As a result of this deformation, unevenness in development may be generated, and there is a fear that a defective image is generated. Further, regardless of the presence of the elastic layer of the developing roller, when the developing roller is kept in contact with the photosensitive drum during transportation, there is a fear that the developing roller surface and the photosensitive drum surface may slide-rub on each other as a result of vibration or shock during transportation, resulting in generation of rubbing marks on the developing roller surface and the photosensitive drum surface. Due to the rubbing marks, there is a fear that a defective image may be generated.
As a construction for solving the above problem, there is a mechanism for retaining, during transportation, the developing unit which holds the developing roller, at a position where the photosensitive drum and the developing roller are separated from each other. Japanese Patent Application Laid-Open No. 2008-261910 discusses a construction in which, at the time of factory shipment of the image forming apparatus with the process cartridge being attached thereto, a separation member for separating the developing roller and the photosensitive drum from each other is placed in the process cartridge (refer to FIG. 10, etc.)
According to Japanese Patent No. 4280770, an image forming apparatus has a mechanism which, when an image is being formed, holds a developing roller and a photosensitive drum in contact with each other, and which, when no image is being formed, separates the developing roller and the photosensitive drum from each other. In this construction, by separating the developing roller from the photosensitive drum, it is possible to suppress deformation of an elastic layer of the developing roller. Further, it is possible to suppress movement of developer from the developing roller to the photosensitive drum when no image is being formed.
In a conventional apparatus, the photosensitive drum unit retaining the photosensitive drum is provided with a regulating portion configured to regulate the position in the axial direction (hereinafter referred to as the longitudinal direction) of the photosensitive drum relative to the developing unit retaining the developing roller. Further, the developing unit is provided with a portion to be regulated. The regulating portion of the photosensitive drum unit and the regulated portion of the developing unit are fitted into each other, whereby the position of the developing unit relative to the photosensitive drum unit is maintained with high accuracy in a longitudinal direction of the developing unit.
However, if a large load is applied to the process cartridge due to vibration or shock during transportation while the developing roller and the photosensitive drum are separated from each other, a load is applied to the regulating portion of the photosensitive drum unit or to the regulated portion of the developing unit. Thus, there is a possibility that the regulating portion or the regulated portion undergoes damage. Or, if, in forming an image, the operation of bringing the developing roller and the photosensitive drum into and out of contact with each other is repeated, the regulating portion and the regulated portion may slidably rub on each other, so that there is a possibility that the regulating portion and the regulated portion may be worn away. When the regulating portion or the regulated portion is damaged or worn away, there is a possibility that the position of the developing unit relative to the photosensitive drum unit cannot be maintained in the longitudinal direction of the developing unit.
Thus, conventionally, to prevent such damage of the regulating portion and the regulated portion, there have been provided a regulating portion and a regulated portion of high strength capable of withstanding shock or wearing during transportation. For this purpose, the regulating portion, etc. has been enlarged or formed of a material of high strength. Thus, in some cases, a size of the process cartridge may be increased in order to secure the requisite space for providing a large regulating or regulated portion. In some cases, there have been limitations regarding the material and configuration of the regulating or regulated portion.